One of the major goals of the USPHS is the regional elimination of measles by the year 2000 which may be achieved due to an increase in immunization rates and implementation of a two dose schedule for measles vaccine. Adverse reactions following immunization receive additional scrutiny as wild type disease diminishes. Last year we initiated a project to investigate the biological basis for post immunization immune thrombocytopenia. To investigate the ability of measles vaccine to induce anti-platelet antibodies, mice were immunized with vaccine (MV), CEF cells, or purified IIbIIA protein. Post immunization, anti -MV, anti-CEF and anti-IIbIIIa reacted with human platelets in ELISA and in western blot, bound to a protein with a Mr of 92-105kD. Rabbit anti-IIbIIIa immunoprecipitated proteins at Mrof 180/135/100 kD from biotinylated vaccine and labeled CEF cells, consistent with reported molecular weights for the chicken vitronectin receptor. Taken together, these findings suggest that chicken cell substrate integrins in vaccine may be responsible in part for inducing anti-platelet antibodies. We are responsible for review of measles vaccine INDs and all issues related to product licensure. Use of the vaccine and changes in approved schedules should be based on data that guarantees vaccine efficacy. Our participation in these collaborative studies allows direct involvement in the evaluation of data that would support changes to the vaccine schedule. This knowledge provides the scientific basis needed for changes in approved use of licensed products and helps to provide guidance in the design of clinical trials for new measles vaccines that would be tested under IND.